Low-Cost Industrial Digital I/O – 60 V, Channel-to-Channel Isolated

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Direct Sensor Connection with Isolation

Isolation, a form of built-in signal conditioning, provides several

advantages, such as an extended voltage range for direct connection to

industrial sensors and actuators. Isolation also improves signal quality

and protects computer circuitry. The PCI-6520 provides channel-to-

channel isolation where every channel is physically and electrically

separated from the others. This isolation breaks ground loops, improves

common-mode voltage and noise rejection, and permits the two parts of

the circuit to be at different voltage levels. Many industrial applications

require isolation to protect the electronics from transient voltage spikes

and provide greater common-mode noise rejection in electrically noisy

environments containing machinery and inductive loads.

Glitch-Free Startup with Programmable

Power-Up States

Using programmable power-up states, you can configure the initial

PCI-6520 output states in software to ensure glitch-free operation when

connected to industrial actuators such as pumps, valves, motors, and

relays. The PCI-6520 holds these I/O states after receiving power, so

your computer can boot and your software application can begin running.

Programmable power-up states are glitch free, meaning the outputs

never go through an incorrect state during power up.

You can configure each individual output line as logic high or logic

low. The PCI-6520 stores the settings in onboard nonvolatile memory

and implements the power-up states automatically after power is

applied to the board.

Watchdog Timers for Fault Detection and Recovery

Watchdog timers are an innovative technology that provide protection

against a wide variety of fault conditions:

• Computer crash – total OS crash

• Application crash – software application ceases to respond

• Driver crash – device driver ceases to respond

• PCI bus failure – communications cease to respond

With watchdogs, the digital outputs go to a safe state when a fault

condition is detected and recover safely after the watchdog timer

expires. Watchdogs are important whenever the module is connected

to actuators such as pumps, valves, motors, and relays. The PCI-6520

monitors the software application; if the application fails to reset the

watchdog timer within the time limit, the device automatically sets

the output lines to a user-defined safe state. The PCI-6520 remains in

the watchdog state until the watchdog timer is disarmed by the

application and new I/O values are written, the PCI-6520 is reset, or

the computer is restarted.

Trigger Your Application

with Change Detection

With change detection, you can automatically trigger your software

application to perform a digital read operation upon a digital change of

state. A digital change of state is defined as the rising edge (0 to 1

transition) or falling edge (1 to 0 transition) on one or more digital lines.

Using change detection, you can monitor for digital events with

minimal processor usage. No polling is necessary because the digital I/O

module generates an interrupt to automatically wake up your

application. Using NI-DAQmx software technology, PCI-6520 notifies the

software application when the event is detected, causing the application

to automatically perform a read operation.

To minimize the effects of noisy input lines, use programmable input

filters in combination with change detection to eliminate spurious

change detection events caused by noise or glitches. NI-DAQmx also

includes multithreaded streaming technology so digital change detection

events can occur independent of other data acquisition activities such as

analog input or output events.

Eliminate Noise with Programmable

Input Filters

Programmable input filters remove noise, glitches, and spikes on inputs,

and also provide debouncing for digital switches and relays. This feature

is important for applications in noisy industrial environments to prevent

false readings caused by noise. You can configure the programmable

input filter for each digital line by setting the filter time in seconds. Any

digital noise, glitch, or spike that is shorter than half of the specified

filter time will be blocked by the digital I/O device, preventing invalid

readings and false triggers for change detection events.

Figure 1. PCI-6520 Hardware Block Diagram